To obtain a better understanding of the structure and functions of the RNA tumor virus RNA-directed DNA polymerase, we propose to carry out a detailed study comparing the properties of the single subunit DNA polymerase (alpha) and the two subunit enzyme (alpha-beta) of avian myeloblastosis virus (AMV). These studies involve 1) development of an in vitro system for selective proteolytic cleavage of the beta subunit resulting in the generation of the alpha subunit and its corresponding smaller fragment. In addition, attempts will be made to cleave the alpha subunit by partial proteolytic digestion in order to separate the DNA polymerase and ribonuclease H sites, 2) development of techniques for isolation of active alpha and beta subunits from alpha-beta DNA polymerase, and 3) further development of the nitrocellulose membrane filter assay technique using alpha and alpha-beta DNA polymerase to investigate the nucleic acid-polymerase complexes formed by these two structurally different polymerases.